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Senior Contributor
Blacksandfarmer
Posts: 899
Registered: ‎08-04-2010
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Re: East Central Iowa

Jim how much rain would you say it takes to activate herbicides? I had both corn and beans sprayed with roundup and a residual herbicide mix last week and so far haven't had a measurable rain. The roundup smoked the weeds but Im concerned the residuals will lose strength... On my way home from work this evening I seen a few pivots running. I would say this crop still has potential here but 2 more weeks of this hot and dry weather and the crop will be in pretty bad shape in the Eastern cornbelt.

Veteran Advisor
Nebrfarmr
Posts: 6,808
Registered: ‎10-25-2010
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Re: East Central Iowa

The agronimist at our local Co-Op told me, if we don't get any rain, to set the pivot to give a half inch, to activate the residual herbicides.  Since a pivot can be set to give any amount you want it to, I'm guessing that is probably what you want for best results.

Senior Advisor
Jim Meade / Iowa City
Posts: 2,527
Registered: ‎04-30-2010
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Rain To Activate Herbicide

I posted a message on this topic in Crop Talk.  It's very interesting, has an illustrative graph, and gives some good perspectives on how to adjust herbicide application to weather conditions.

The short answer from ISU is 1/2" gets you about 85-90% effectiveness on foxtail, 1" gets 100%.  1/4" isn't much better than nothing. 

I'm in the "not much better than nothing" stage. 

Veteran Advisor
Nebrfarmr
Posts: 6,808
Registered: ‎10-25-2010
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Re: Rain To Activate Herbicide

Do you know if that inch has to come all at once?

I mean, if one gets 1/4 inch, 3 days in a row, is that the equivalent of a 3/4 inch rain, to activate the herbicide?

Senior Advisor
Jim Meade / Iowa City
Posts: 2,527
Registered: ‎04-30-2010
0

Re: Rain To Activate Herbicide

I don't remember what the article said on that, if anything.  It's in Crop Talk.

Esteemed Advisor
sw363535
Posts: 4,769
Registered: ‎07-18-2011
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Re: Rain To Activate Herbicide

Would be better if it was 3/4 inch at once.

Some Herbicides needs to be pushed to sprouting depth of weeds.  40/100 on three different days probably would not be as affective.

sw